Generally corona-discharge electrode assemblies are arranged in alternation with collecting-electrode assemblies, sheets, the corona-discharge electrode elements being tensioned by suspended weights or by special frames. The last-mentioned arrangement has the advantage that the corona discharge electrodes can be rapped effectively to clean the same.
All of the corona-discharge electrode elements must be tensioned as uniformly as possible and in such a manner that a safety margin from the ultimate stress is maintained under operating conditions. The tensioning operation, which involves a high labor expenditure, because of the large numbers of electrode elements, must be performed as efficiently as possible.
When the corona-discharge electrode elements (wires or strips) are tensioned by wedges against the frame, which is composed of tubes (German Pat. No. 968,440), the tensioning procedure is very time-consuming because each of the corona-discharge electrode elements must be re-tensioned several times in order to ensure uniform tension and because there is always a danger that individual corona-discharge electrode elements may be overloaded as the wedges are driven.
It is also known to secure corona-discharge wires, like the strings of a harpsichord, in a grid frame consisting of tubular elements and to solder the wires to the frame (German Utility Model 16 00 421). In this case also it is particularly difficult to achieve uniform tension and the operation may result in too-tightly tensioned corona discharge wires and in loose wires, which tend to break, particularly under cyclic loads.
Finally, corona-discharge electrode elements can have specially designed end portions (German Pat. No. 2,044,738), which are arranged in bores of holding frames and to tension these electrodes in that a wedge is driven between the frame and the abutment provided at the end of the corona discharge electrode, which is subsequently welded to the frame, while this practice results in a much-improved manipulation, a sufficiently uniform tension is not always achieved with this method, which also can result in excessively tensioned corona-discharge electrode elements as well as corona-discharge electrode elements which are not sufficiently tensioned.
Specifically, in this latter method the tension of corona-discharge electrode elements tensioned by different workers may vary, so that variations and disadvantages regarding the corona-discharge and cleaning properties result. Besides, the corona-discharge electrode elements cannot always be tensioned and secured by this method so that their corona-discharge points have the intended orientation relative to the tensioning frame.
In the aforementioned copending application, there is described a system which at least partly overcomed the aforedescribed disadvantages by the use of a caliper-type tool, one arm of which engages the corona-electrode element while the other arm serves to tension the element against a bar of the support or holding frame.